Porous materials are widely used for catalysts, adsorbents, surface active agents, and the like. A porous material is a material having micropores of a certain shape, and, among them, a porous material having micropores the diameter of which is 2 nanometer (hereinafter the abbreviated term nm to be used) or less is called a microporous material, and that the diameter of which is 2-50 nm is called a mesoporous material. As a microporous material, for example, zeolite is well known. Zeolite is a crystalline material in which such metal atoms as Si and Al are bonded via oxygen, having micropores of a certain shape, and is used, by utilizing said micropores, for example, as a cracking catalyst to crack heavy oil to gasoline, or as a molecular sieve adsorbent not passing branched alkanes but passing linear alkanes only.
Further in the recent years, the porous material having larger void, that is, the mesoporous material is proposed for improvement of catalytic function and realization of a new function, and the preparation of mesoporous materials consisting of metal oxides such as silica is widely studied. The mesoporous material represented by mesoporous silica is prepared by forming metal oxide thin film around the template which is self-organized organic molecule aggregate such as surface active agent micelles and inorganic or organic nanoparticles, and removing said template. The pore structure of mesoporous material can be controlled by controlling the size and arrayed structure of the material used for a template, and mesoporous materials with randomly dispersed mesopores, those with regularly arrayed mesopores, or those with spherical mesopores regularly arrayed in three dimension, and many others have been realized.
Although mesoporous materials have no regularity on atomic level, they are the crystals of new type so far not existent in which the voids of mesoscale are regularly arrayed, and are expected hereafter in the active role as industrial materials as adsorbing and separating materials (the materials to adsorb specific molecules in voids and separate them), catalysts, and surface active agents. Their applications in various fields are anticipated very much such as utilization as new electron device materials by introducing the aggregate of various atoms and molecules into voids.
Here, the size of a void formed between a nanoparticle and a mesopore enclosing it is quite important as the quantity to characterize the space of chemical reaction for catalytic reactions and material syntheses, and the fields of material adsorption or material enclosing. That is, it is predictable that a structure having an adjustable void space near a nanoparticle, and the structure having as a constituent said structure can be a catalyst of extremely high efficiency compared with conventional catalysts, can give the selectivity of chemical species involved in chemical reaction, can be a catalyst for the chemical reaction for which no catalyst has so far been available, or can be used as the basis for preparation of a nanomaterial required for nanodevice.
For example, since the photocatalytic reaction takes place on the surface of photocatalyst such as titanium oxide, many studies have been made to realize the photocatalyst of high efficiency by increasing the surface area by converting photocatalyst to a nanoparticle. However, since nanoparticles coagulate by Van der Waals force, the chemical species involved in catalytic reaction cannot be adsorbed on a nanoparticle, thereby an expected result cannot be realized. That is, a photocatalyst of high efficiency cannot be realized because an adjustable void space does not exist near a nanoparticle.
If a void space can be made near a nanoparticle, then the chemical species involved in catalytic reaction can be adsorbed on a catalyst nanoparticle, and a photocatalyst of high efficiency can be realized. If also the size of a void space near a nanoparticle can be controlled, in another word, if an adjustable void space can be formed near a nanoparticle, then the molecular species to be adsorbed can be controlled, thereby the selectivity of chemical species involved in catalytic reaction can be realized. Since also the structure having as a constituent a structure having an adjustable void space near a nanoparticle can array specific molecular species based on the shape of structure, it can be the catalyst for the chemical reaction for which no catalyst has so far been available, and can be used as the basis to prepare the nanomaterial required for nanodevice.
The conventional porous material having a void space near a nanoparticle is the combination of a mesoporous material and a nanoparticle made of a metal or a semiconductor. The conventional method to form a nanoparticle inside mesoporous material is to introduce the reactive gas as the starting material for a nanoparticle into mesoporous material, let it react and decompose, and to have a nanoparticle grow inside the micropore of mesoporous material. However, in the nanoparticle-mesoporous material complex prepared by said method, the particle diameter of a nanoparticle differs by the location inside mesoporous material, and therefore it is quite difficult to control particle diameter. For this reason, it is extremely difficult by the prior art to prepare porous material having the controlled nano void space near a nanoparticle. In other words, it has been difficult by the prior art to prepare the structure having the controlled nano void space near a nanoparticle, and structures having said structure as a constituent unit.